Search

Polar hydrogen deposits on the Moon provide evidence that its spin axis has shifted; analysis of the locations of these deposits and of the lunar figure suggests that the shift occurred as a result of changes in the Moon's moments of inertia caused by a low-density thermal anomaly beneath the Procellarum region. Polar wandering on the Moon Matthew Siegler and co-authors show that the polar hydrogen deposits detected on the Moon by orbital neutron spectroscopy pose something of a mystery: the spatial distribution of hydrogen, which is thought to arise from the presence of water ice, does not match that expected from present-day lunar temperatures. The explanation may lie in the phenomenon known as 'true polar wander', in which a reference point on a solid body rotates with respect to its spin axis. Based on an analysis of polar deposit locations and of the lunar figure, the authors suggest that the shift occurred as a result of changes in the Moon's moment of inertia caused by a low-density thermal anomaly beneath the Procellarum region. Procellarum was most geologically active early in lunar history, which would imply that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. The earliest dynamic and thermal history of the Moon is not well understood. The hydrogen content of deposits near the lunar poles may yield insight into this history, because these deposits (which are probably composed of water ice) survive only if they remain in permanent shadow. If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed. The polar hydrogen deposits have been mapped by orbiting neutron spectrometers.sup.1,2,3, and their observed spatial distribution does not match the expected distribution of water ice inferred from present-day lunar temperatures.sup.4,5. This finding is in contrast to the distribution of volatiles observed in similar thermal environments at Mercury's poles.sup.6. Here we show that polar hydrogen preserves evidence that the spin axis of the Moon has shifted: the hydrogen deposits are antipodal and displaced equally from each pole along opposite longitudes. From the direction and magnitude of the inferred reorientation, and from analysis of the moments of inertia of the Moon, we hypothesize that this change in the spin axis, known as true polar wander, was caused by a low-density thermal anomaly beneath the Procellarum region. Radiogenic heating within this region resulted in the bulk of lunar mare volcanism.sup.7,8,9,10,11 and altered the density structure of the Moon, changing its moments of inertia. This resulted in true polar wander consistent with the observed remnant polar hydrogen. This thermal anomaly still exists and, in part, controls the current orientation of the Moon. The Procellarum region was most geologically active early in lunar history.sup.7,8,9, which implies that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. Our hypothesis provides an explanation for the antipodal distribution of lunar polar hydrogen, and connects polar volatiles to the geologic and geophysical evolution of the Moon and the bombardment history of the early Solar System., Author(s): M. A. Siegler [sup.1] [sup.2] , R. S. Miller [sup.3] , J. T. Keane [sup.4] , M. Laneuville [sup.5] , D. A. Paige [sup.6] , I. Matsuyama [sup.4] , [...]

The origin of lunar magnetic anomalies (1-5) remains unresolved after their discovery more than four decades ago. A commonly invoked hypothesis is that the Moon might once have possessed a thermally driven core dynamo (3), but this theory is problematical given the small size of the core and the required surface magnetic field strengths (6). An alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins (7), but many magnetic anomalies exist that are not associated with basin antipodes. Here we propose a new model for magnetic field generation, in which dynamo action comes from impact-induced changes in the Moon's rotation rate. Basin-forming impact events are energetic enough to have unlocked the Moon from synchronous rotation (8), and we demonstrate that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core-mantle boundary (9), could have powered a lunar dynamo. Predicted surface magnetic field strengths are on the order of several microteslas, consistent with palaeomagnetic measurements (5), and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins., Magnetic field measurements of the Moon from orbit demonstrate that portions of its crust are strongly magnetized (1), and palaeomagnetic analyses of lunar rocks show that some samples possess stable [...]

This article, titled "DES SOLUTIONS D'ICI POUR FAIRE FACE À L'ÉBULLITION CLIMATIQUE," provides a comprehensive overview of various solutions to address the challenges posed by climate change. It highlights inspiring and relevant examples of improvements that can be made to enhance the climate resilience of both urban and rural environments. The article also explores plausible climate scenarios for the end of the century, emphasizing the investments required to ensure the health and safety of populations and ecosystems. It acknowledges the increasing frequency and intensity of extreme weather events, such as ice storms, floods, wildfires, and heatwaves, which have become the new normal in Quebec. Additionally, it discusses less tangible but equally harmful phenomena, including erosion, invasive species, and soil and water acidification. The article concludes by presenting innovative solutions to reduce Quebec's greenhouse gas emissions. It emphasizes the need for a multisectoral approach to address the dual challenges of the climate crisis and biodiversity protection. The article is part of the mission of Réseau Environnement, an organization that aims to guide public policies and address the climate crisis. The article also mentions the upcoming Quebec Environmental Technologies Exhibition (STEQ) in April 2024, which will showcase promising environmental innovations. The article encourages the sharing and implementation of these solutions to mitigate the effects of climate change and promote climate adaptation within communities. [Extracted from the article]

Phosphorus (P) is a crucial structural component of living systems and central to modern bioenergetics. P cycles through terrestrial geochemical reservoirs via complex physical and chemical processes. Terrestrial life has altered these fluxes between reservoirs as it evolved, which is why it is of interest to explore planetary P flux evolution in the absence of biology. This is especially true, since environmental P availability affects life's ability to alter other geochemical cycles, which could then be an example of niche construction. Understanding how P reservoir transport affects environmental P availability helps parameterize how the evolution of P reservoirs influenced the emergence of life on Earth, and potentially other planetary bodies. Geochemical P fluxes likely change as planets evolve, and element cycling models that take those changes into account can provide insights on how P fluxes evolve abiotically. There is considerable uncertainty in many aspects of modern and historical global P cycling, including Earth's initial P endowment and distribution after core formation and how terrestrial P interactions between reservoirs and fluxes and their rates have evolved over time. We present here a dynamical box model for Earth's abiological P reservoir and flux evolution. This model suggests that in the absence of biology, long term planetary geochemical cycling on planets similar to Earth with respect to geodynamism tends to bring P to surface reservoirs, and biology, including human civilization, tends to move P to subductable marine reservoirs., (© 2022. The Author(s).)

Nitrogen is the major component of Earth's atmosphere and plays important roles in biochemistry. Biological systems have evolved a variety of mechanisms for fixing and recycling environmental nitrogen sources, which links them tightly with terrestrial nitrogen reservoirs. However, prior to the emergence of biology, all nitrogen cycling was abiological, and this cycling may have set the stage for the origin of life. It is of interest to understand how nitrogen cycling would proceed on terrestrial planets with comparable geodynamic activity to Earth, but on which life does not arise. We constructed a kinetic mass-flux model of nitrogen cycling in its various major chemical forms (e.g., N 2 , reduced (NH x ) and oxidized (NO x ) species) between major planetary reservoirs (the atmosphere, oceans, crust, and mantle) and included inputs from space. The total amount of nitrogen species that can be accommodated in each reservoir, and the ways in which fluxes and reservoir sizes may have changed over time in the absence of biology, are explored. Given a partition of volcanism between arc and hotspot types similar to the modern ones, our global nitrogen cycling model predicts a significant increase in oceanic nitrogen content over time, mostly as NH x , while atmospheric N 2 content could be lower than today. The transport timescales between reservoirs are fast compared to the evolution of the environment; thus atmospheric composition is tightly linked to surface and interior processes. Key Words: Nitrogen cycle-Abiotic-Planetology-Astrobiology. Astrobiology 18, 897-914.

We propose a metric which can be used to compute the amount of heritable variation enabled by a given dynamical system. A distribution of selection pressures is used such that each pressure selects a particular fixed point via competitive exclusion in order to determine the corresponding distribution of potential fixed points in the population dynamics. This metric accurately detects the number of species present in artificially prepared test systems, and furthermore can correctly determine the number of heritable sets in clustered transition matrix models in which there are no clearly defined genomes. Finally, we apply our metric to the GARD model and show that it accurately reproduces prior measurements of the model's heritability.

Maps of crustal thickness derived from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission revealed more large impact basins on the nearside hemisphere of the Moon than on its farside. The enrichment in heat-producing elements and prolonged volcanic activity on the lunar nearside hemisphere indicate that the temperature of the nearside crust and upper mantle was hotter than that of the farside at the time of basin formation. Using the iSALE-2D hydrocode to model impact basin formation, we found that impacts on the hotter nearside would have formed basins with up to twice the diameter of similar impacts on the cooler farside hemisphere. The size distribution of lunar impact basins is thus not representative of the earliest inner solar system impact bombardment.